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| United States Patent |
5,281,651
|
|
Arjunan
, et al.
|
January 25, 1994
|
Compatibilization of dissimilar elastomer blends using
ethylene/acrylate/acrylic acid terpolymers
Abstract
This invention relates to a compatibilized rubber composition and a process
for compatibilizing dissimilar rubber blends comprising blending an
ethylene/acrylate/acrylic acid terpolymer with 2 or more different
rubbers, selected from the group including, but not limited to, EPR, EPDM,
CR, NBR, SBR and NR.
| Inventors:
|
Arjunan; Palanisamy (Dayton, NJ);
Kusznir; Roma B. (Flushing, NY)
|
| Assignee:
|
Exxon Chemical Patents Inc. (Linden, NJ)
|
| Appl. No.:
|
827772 |
| Filed:
|
January 29, 1992 |
| Current U.S. Class: |
524/519; 524/522; 525/194; 525/195; 525/196; 525/211; 525/215; 525/221 |
| Intern'l Class: |
C08L 009/02; C08L 011/02; C08L 007/00; C08L 023/26 |
| Field of Search: |
525/221,211,215,196
524/522,519
|
References Cited
U.S. Patent Documents
| 3645934 | Feb., 1972 | Caywood, Jr. | 260/5.
|
| 4307204 | Dec., 1981 | Vidal | 521/140.
|
| 4397987 | Aug., 1983 | Cornell | 525/75.
|
| 4433073 | Feb., 1984 | Sano et al. | 524/222.
|
| 4607074 | Aug., 1986 | Hazelton et al. | 524/425.
|
| 4611031 | Sep., 1986 | Galluccio et al. | 525/310.
|
| 4639487 | Jan., 1987 | Hazelton et al. | 525/221.
|
| 4851468 | Jul., 1989 | Hazelton et al. | 525/215.
|
| 4957974 | Sep., 1990 | Ilenda et al. | 525/301.
|
| 5140072 | Aug., 1992 | Takeshita | 525/215.
|
| Foreign Patent Documents |
| 56-047441 | Apr., 1981 | JP | 525/236.
|
| 57-135844 | Apr., 1982 | JP.
| |
Primary Examiner: Seccuro, Jr.; Carman J.
Attorney, Agent or Firm: Bell; Catherine L.
Claims
What is claimed is:
1. A process for compatibilizing elastomer blends consisting essentially of
blending a random terpolymer comprising ethylene
and about 4 to 40 weight % acrylate or methacrylate and about 1 to 10
weight % acrylic acid or methacrylic acid with an elastomer blend
comprising at least one first elastomer selected from the group consisting
of ethylene-propylene rubber, styrene-butadiene rubber, natural rubber and
ethylene-propylene-diene rubber, and at least one second elastomer
selected from the group consisting of neoprene rubber and nitrile rubber
optionally, carbon black, and optionally, a vulcanization system.
2. The process of claim 1 wherein the first elastomer is selected from the
group consisting of ethylene-propylene rubber and ethylene propylene-diene
rubber.
3. The process of claim 1 wherein the acrylate of the terpolymer is
methacrylate.
4. The process of claim 1 wherein the acrylic acid of the terpolymer is
present from 2 to 8 wt. %, and the acrylate of the terpolymer is present
at 5 to 35 wt. % based upon the weight of the terpolymer.
5. The process of claim 1 wherein the terpolymer is present at from 1 to 65
phr.
6. The process of claim 1 wherein the terpolymer is present at from 5 to 20
phr.
7. A composition of matter consisting essentially of: a random terpolymer
comprising ethylene and about 4 to 40 weight % acrylate or methacrylate
and about 1 to 10 weight % acrylic acid or methacrylic acid,
an elastomer blend comprising at least one first elastomer selected from
the group consisting of ethylene-propylene rubber, styrene-butadiene
rubber, natural rubber and ethylene-propylene-diene rubber, and at least
one second elastomer selected from the group consisting of neoprene rubber
and nitrile rubber;
optionally, carbon black, and
optionally, a vulcanization system.
8. A composition of matter consisting essentially of a blend of a random
terpolymer comprising ethylene and about 4 to 40 weight % acrylate or
methacrylate and about 1 to 10 weight % acrylic acid or methacrylic acid,
an elastomer blend comprising at least one first elastomer selected from
the group consisting of ethylene-propylene rubber, styrene-butadiene
rubber, natural rubber and ethylene-propylene-diene rubber, ad at least
one second elastomer selected from the group consisting of neoprene rubber
and nitrile rubber,,
carbon black,
a vulcanization system and one or more of other fillers, lubricants,
plasticizers, tackifiers, coloring agents, blowing agents or antioxidants.
9. The composition of claim 9 or 10 where the first elastomer is selected
from the group consisting of ethylene-propylene rubber and ethylene
propylene-diene rubber.
10. A compatibilized elastomer blend consisting essentially of:
(A) polychloroprene;
(B) ethylene-propylene rubber, or ethylene propylene-diene rubber;
(C) a random terpolymer comprising ethylene and about 4 to 40 weight %
acrylate or methacrylate and about 1 to 10 weight % acrylic acid or
methacrylic acid;
(D) optionally carbon black,
(E) optionally a vulcanization system; and
(F) optionally one or more of other fillers, lubricants, plasticizers,
tackifiers, coloring agents, blowing agents or antioxidants.
11. The composition of claim 8, 9 or 10 formed into an article.
12. The composition of claim 8, 9 or 10 formed into a power transmission
belt, tire portion, belt, hose, or air spring.
13. The composition of claim 10 wherein the polychloroprene is present at
30 to 90 parts by weight.
14. The composition of claim 8, 9 or 10 wherein the carbon black is present
at about 3 to 50 phr.
15. The process of claim 1 further including other fillers, lubricants,
plasticizers, tackifiers, coloring agents, blowing agents or antioxidants.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to the field of compatibilization technology. In
particular, this invention relates to the use of
ethylene/methacrylate/acrylic acid terpolymers as compatibilizers for
dissimilar elastomer blends.
2. Description of the Related Art
A considerable amount of research has been made over the last several years
with a view to obtaining new polymeric materials with enhanced specific
attributes for specific applications or a better combination of different
attributes. Much attention is currently being devoted to the simplest
route for combining outstanding properties of different existing polymers,
that is, formation of polymer blends. Although increasing numbers of
miscible blends are reported in the literature [D. R. Paul et. al., J.
Macromol. Sci., Rev. Macromol. Chem., C-8:109 (1980)], most polymers are
nonetheless immiscible thus leading to heterophase polymer blends. In
general, "compatibility (miscibility) is the exception, immiscibility is
the rule" (Dobry and Boyer-Kawenski, J. Polymer Science, 1947).
There are two widely useful types of elastomer blends: single phase and two
phase blends. The single phase blend is miscible. The term miscibility
does not imply ideal molecular mixing but suggests that the level of
molecular mixing is adequate to yield macroscopic properties expected of a
single-phase material.
The formation of two-phase elastomer blend is not necessarily an
unfavorable event since many useful properties, characteristic of a single
phase, may be preserved in the blend composition while other properties
may be averaged according to the blend composition. Proper control of
overall elastomer blend morphology and good adhesion between the phases
are in any case required in order to achieve good mechanical properties.
The elastomer blend components that resist gross phase segregation and/or
give desirable blend properties are frequently said to have a degree of
"compatibility" even though in a thermodynamic sense they are not
"miscible". It should be emphasized that "compatibility" and "miscibility"
are two different terms. Compatibilization means the absence of separation
or stratification of the components of the polymeric alloy during the
expected useful lifetime of the product (Gaylord, N. G., in "Copolymers,
Polyblends and Composites", Advances in Chemistry Series 142, American
Chemical Society: Washington, D.C., 1975, p. 76). "Technological
compatibilization", according to Coran and co-workers [Rubber Chem.
Technol., 56, 1045 (1983)] is "the result of a process or technique for
improving ultimate properties by making polymers in a blend less
incompatible; it is not the application of a technique which induces
"thermodynamic compatibility", which would cause the polymers to exist in
a single molecularly blended homogeneous phase".
It is well established that the presence of certain polymeric species,
usually block or graft copolymers with the right structure, can indeed
result in compatibilization of an immiscible elastomer blend because of
their ability to alter the interfacial situation. Such, species as a
consequence, are often referred to as "compatibilizers" or "interfacial
agents" which is analogous to the term "solubilization used in the colloid
field to describe the effect surfactants have on the ability to mix oil
and water (McBain et. al., "Solubilization and Related Phenomena",
Academic Press, New York, 1955). Such "compatibilizers" can be either
preformed and added to the binary blend or formed "in situ" during the
blending process.
The role of the compatibilizer in an elastomer blend is manifold: (1)
reduce the interfacial energy between the phases, (2) permit a finer
dispersion during mixing, (3) provide a measure of stability against gross
segregation, and (4) result in improved interfacial adhesion (G. E. Molau,
in "Block Copolymers", Ed by S. L. Agarwal, Plenum, N.Y., 1970, p. 79).
Two elastomers form a compatible mixture when they have at least one of the
following characteristics:
Segmental structural identity. For example, a graft or block copolymer of
butadiene and styrene is compatible with either polybutadiene or
polystyrene.
Miscibility or partial miscibility with each other. Solubility parameter (
) difference<1, generally<0.2 units. For example, poly (vinyl chloride),
PVC, poly (ethylacrylate), PEA, poly (methylacrylate), PMMA, have
solubility parameters in the 9.4-9.5 range and form compatible mixtures.
Although, the structure of nitrile rubber, NBR is entirely different from
those of PVC, PMMA, PEA, it has a similar solubility parameter 9.5 and is
compatible with these three polymers.
Functional groups capable of generating covalent, ionic, donor-acceptor or
hydrogen bonds between the polymers.
Compatibilization of dissimilar elastomer blends is an area of active
interest from both technological and scientific points of view. Many of
the synthetic and natural elastomers have good properties that when
combined with other rubbers of similar or complementary properties may
yield desirable traits in the products.
Neoprene or polychloroprene rubber (CR) has been the material of choice in
most power transmission belts, due to its unique combination of
properties: ozone resistance, oil resistance, toughness, dynamic flex
life, good adhesion to other materials and heat resistance up to
100.degree. C. In the past, CR belts have kept pace with the needs of the
automotive industry, but recently there is a need for new materials for
more demanding applications. First of all, CR belts are encountering
greater heat duress in service due to increasing underhood temperatures
(up to 150.degree. C.). Secondly, to meet automotive industry's longer
warranty periods ("100,000 mile target"), the CR belts must have a lower
failure rate with high mean life, even when high temperatures are not
encountered. To meet these emerging needs, improvements in heat, ozone,
and cut growth resistance of neoprene belts are desirable. The above
requirement for neoprene belts could be satisfied by blending with
polyolefin elastomers such as ethylene/propylene rubber (EPR) or
ethylene/propylene/diene terpolymer (EPDM) which have better heat/ozone
and cut growth resistance. As such, however, these neoprene/EPR or EPDM
blends are incompatible.
Nitrile rubber (NBR) is used in automobiles because of its resistance to
fuels, a variety of oils and other fluids over a wide range of
temperatures. However, nitrile rubber, as such cannot be used in specific
applications requiring high heat and ozone resistance. The poor ozone
resistance and heat aqeinq properties of NBR (which is a random copolymer
of acrylonitrile and butadiene) are believed to be the result of
unsaturation in the backbone of the polymer which permits scission of the
polymer chain to occur under certain adverse conditions.
EPDM rubber, on the other hand, has good heat ageing and ozone resistance
because, its unsaturation sites are in side chains which render the
polymer generally immune to scission of the backbone chain. However, these
EPR or EPDM rubbers have poor oil resistance even in the cured state. It
is desirable to achieve the best properties of both NBR and EPDM rubber,
i.e. improved heat, ozone and oil resistance by blending the said rubbers
synergistically. Such NBR/EPDM blends could find numerous applications in
the automobile industry. As such, however, these NBR/EPDM blends are
incompatible, because of the polarity difference between the blend
components.
It is known in the art that the resistance of cured unsaturated elastomers
such as polybutadiene or polyisoprene to chemical attack from ozone and
oxygen can be enhanced by forming a blend thereof with minor amounts of an
ethylene/propylene/diene terpolymer and co-vulcanizing the blend. This
development takes advantage of the inherent resistance of the olefin/diene
terpolymer to chemical attack and imparts this property into co-vulcanized
blend.
However, the use of olefin/diene terpolymers in blends with other
elastomers is often limited to those other elastomers which have a mutual
compatibility and comparable cure rate behavior with respect to the
olefin/diene terpolymer. Thus, whereas highly unsaturated elastomers such
as polybutadiene or polyisoprene may be, in some cases reasonably
compatible with olefin/diene elastomers and may be readily co-vulcanized
because of the high availability of sites of ethylenic unsaturation, other
elastomers such as polychloroprene, butadiene/acrylonitrile copolymers
(nitrile) and like materials containing polar groups along the chain
and/or a relatively low degree of ethylenic unsaturation are not so
readily co-vulcanized. In the case of blends with these latter elastomers,
chemical resistance may be improved due to the influence of the
olefin/diene terpolymer, but often at the expense of a lowering of
physical properties such as tensile strength, elongation, modulus and/or
abrasion resistance of the co-vulcanizate as compared with the cured
elastomer itself.
Furthermore, many rubber compounds contain carbon black as a filler to
increase strength, rigidity and other factors. Thus, a rubber blend must
also be able to incorporate carbon black to be of use in the automotive
industry. However, for blends of dissimilar elastomers, problems can arise
in achieving optimum carbon black distribution between the microphases of
the final product. In blends of elastomers that differ significantly in
terms of unsaturation or viscosity, carbon black tends to locate
preferentially in the higher unsaturation or lower viscosity phase.
Carbon black aggregates may also transfer from one elastomer to another
during mixing if they are contained in a polymer of low unsaturation, or
in a masterbatch with high extender oil content and relatively low heat
history. Polarity is also a factor controlling carbon black migration in
elastomer blends. Carbon black has been shown to transfer or migrate
between natural rubber (NR, polyisoprene), and polychloroprene (CR).
However, it was observed that most of the carbon black in such a NR/CR
blend remained at the interface--Marsh, P. A. Rubber Chem. and Tech.
41,344 (1968). Other research has shown undesirable displacement of the
carbon black by more polar elastomers, Craig P. and Fowler R. B., Rubber
World, 146(6), 79, (1962).
Thus, it would be of great importance to the art if a compatibilizer for
dissimilar rubber blends such as CR/EPDM, NBR/EPDM could be found. It
would be of further advantage to the art if this compatibilizer also
caused delocalized dispersion of the carbon black in the above dissimilar
rubber blends.
Use of an ethylene/acrylate/acrylic acid terpolymer as a compatibilizer for
rubber blends is not known in the technology. Of tangential interest may
be U.S. Pat. No. 4,607,074 to Hazelton where a cured rubber, an uncured
rubber and a polyolefin are blended. The polyolefin is taught to be a
copolymer of ethylene and unsaturated esters of C.sub.1 to C.sub.4
monocarboxylic acids. Hazelton does not disclose a terpolymer of
ethylene/acrylate/acrylic acid.
In addition, U.S. Pat. No. 4,307,204 to DuPont discloses an expandable,
curable elastomeric sponge composition based on ethylene/propylene/diene
terpolymer (EPDM) elastomer or polychloroprene elastomer, which
composition further contains a minor amount of an ionomer resin which is
an ethylene polymer or copolymer containing at least about 50 mole percent
acid functional groups, which groups are at least 50% neutralized by metal
ions. These acid-modified ethylene polymers, which may also include
acid-modified EPDM terpolymers, are disclosed to improve the balance of
curing and expanding properties of the polymer composition when used to
prepare cured expanded materials.
None of the aforementioned disclosures addresses the development of a
compatibilized polychloroprene/EPDM or EPR or nitrile rubber/EPDM or EPR
blends which not only exhibit improved resistance to ozone or oxygen
attack and improved heat stability, but also exhibit a retention and in
some cases improvement of important physical properties such as tensile
strength, elongation, modulus and resistance to abrasion. Also, the said
references do not address the issue of carbon black distribution in a
binary, dissimilar elastomer blends and ways to improve the distribution
of carbon black in both phases of such blends.
SUMMARY OF THE INVENTION
A new compatibilizer for dissimilar elastomer blends is disclosed herein.
Ethylene/acrylate/acrylic acid terpolymers, have been found to
compatibilize dissimilar elastomer blends, including, but not limited to,
neoprene/EPDM, nitrile/EPDM blends, etc., by improving the properties of
the said blends. The same compatibilizer also acts to cause delocalized
dispersion of carbon black in a dissimilar elastomer blend. The present
invention provides for neoprene/EPDM or EPR and nitrile/EPDM or EPR blend
compositions and vulcanizates thereof having improved heat, ozone and cut
growth resistance comprising a compatibilized blend of neoprene/EPDM (or
EPR), or nitrile/EPDM (or EPR) and 5 to about 20% by weight, based on the
content of total elastomer in the composition, of an
ethylene/acrylate/acrylic acid terpolymer. The blends of this invention
may be readily co-vulcanized and formed into shaped, heat, ozone, cut
growth and oil resistant articles such as automotive drive belts and
automotive hoses which not only exhibit improved heat, ozone and cut
growth resistance but also have retained or enhanced physical properties
such as abrasion resistance, modulus, elongation and tensile strength.
It has been found that terpolymers with the general structure
ethylene/acrylate/acrylic acid "E/AC/AA", provide excellent mechanical
compatibility with a wide range of polymers, both polar and nonpolar
types. These terpolymers can be used to modify the adhesive and mechanical
properties of dissimilar plastics, and rubber blends. The terpolymer is
blended into the dissimilar, plastic, or rubber at anywhere from 1 to 65
phr, during the compounding of the blend preferably from 5 to 20 phr.
The ethylene/acrylate/acrylic acid (E/AC/AA) terpolymers used in this
invention are excellent compatibilizers for nitrile rubber and
ethylene/propylene rubber (NBR/EPR) blends, including nitrile rubber and
ethylene/propylene/diene (NBR/EPDM) blends. The E/AC/AA terpolymers are
also excellent compatibilizers for neoprene/EPR and neoprene/EPDM blends.
Using the E/AC/AA terpolymer as a compatibilizer in these rubber blends
also has the added advantage of causing delocalized dispersion of the
carbon black. As previously discussed, carbon black tends to localize in
one phase of a binary, dissimilar elastomer blend. This usually is
undesirable and results in poor product properties. The E/MA/AA terpolymer
causes the carbon black to be more uniformly dispersed in the components
of the blend.
The ethylene/acrylate/acrylic acid terpolymer useful in this invention
comprises a random copolymer of: ethylene, a lower alkyl acrylate, and an
acrylic acid. The terpolymer has an acrylate content of from about 4% to
about 30%, and an acrylic acid content of from about 1% to about 10%, by
weight based upon the weight of the E/AC/AA terpolymer with the remainder
being ethylene. The E/AC/AA terpolymer is preferably produced by well
known free radical initiated polymerization methods.
The acrylates useful in this invention are lower alkyl; i.e., containing
one to four carbon atoms, esters and include methacrylates. Methyl
acrylate is particularly preferred.
The term acrylic acid is herein defined to include methacrylic acid.
The rubbers and the terpolymer, E/AC/AA, may be blended, formed, or
otherwise mixed by any one of a number of suitable methods.
The rubbers useful in this invention include ethylene/ propylene rubber,
(EPR); ethylene/propylene/diene terpolymer, (EPDM);
Poly(butadiene-co-acrylonitirile), -nitrile rubber (NBR); polychloroprene,
(neoprene or CR rubber); styrene/butadiene rubber (SBR), and natural
rubber (NR).
The EPR's useful in this invention are random copolymers of ethylene and
propylene where the copolymer has an ethylene content of 30 to 85 wt. %,
based upon the weight of the copolymer. The EP copolymer can be produced
by the well known free radical polymerization method.
The EPDM Rubber useful in this invention are random copolymers
ethylene/propylene/and a diene, where the ethylene is present at 35-80 wt.
%, and the diene is present at 0 to 15 wt. %, based upon the weight of the
copolymer. The EPDM polymer can be produced by the well known free radical
polymerization method. The dienes useful in producing EPDM copolymers are
typically 1,4-hexadiene, cycloalkylidene norbornenes, etc.
The nitrile rubbers useful in this invention are random copolymers of a
major proportion of butadiene and a minor proportion of acrylonitrile and
are typically produced by the free radical polymerization method.
The neoprene rubbers useful in this invention are polymers of chloroprene.
These can be produced by the well known free radical polymerization
method.
In particular, the terpolymer of this invention is useful for
compatibilizing Neoprene/EPR; neoprene/EPDM; nitrile/ EPR; nitrile/EPDM;
neoprene/EPR/carbon black; neoprene/ EPDM/carbon black; nitrile/EPR/carbon
black and nitrile/EPDM/carbon black blends.
DETAILED DESCRIPTION OF THE INVENTION
This invention provides a process for compatibilizing rubber blends
comprising blending an ethylene/acrylate/acrylic acid terpolymer with two
or more different rubbers.
This invention further relates to compatibilized compositions of dissimilar
rubber blends, a terpolymer of ethylene/acrylate/acrylic acid and
optionally carbon black.
In essence, this invention provides a new approach for compounding rubber
blends using an ethylene/acrylate/ acrylic acid terpolymer as the
compatibilizer. This approach also causes a delocalized dispersion of
carbon black in the dissimilar elastomers blend. In particular, we have
found that an ethylene/methacrylate/acrylic acid terpolymer is an
excellent agent for compatibilizing neoprene/ethylene-propylene rubber;
neoprene/ethylene-propylene-diene; nitrile rubber/ethylene-propylene
rubber; and nitrile rubber/ethylene-propylene-diene blends. The E/AC/AA
terpolymer, particularly ethylene/methacrylate/acrylic acid, also causes a
highly desirable delocalization of carbon black added to the above blends.
E/AC/AA terpolymers useful in the present invention are sold by EXXON
CHEMICAL CO. under the name Escor Acid Terpolymers. In particular, Escor
ATX 350 and Escor ATX 320 are very useful.
The E/AC/AA terpolymers, as mentioned earlier, comprise random copolymers
of ethylene, a lower alkyl acrylate, particularly methyl acrylate, and an
acrylic acid. The acrylate and acrylic acid, in the singular, refer to
both a single form and combinations of different forms of the compounds.
Acrylic acid is herein further defined to include methacrylic acid.
In the preferred embodiment, the E/AC/AA terpolymer comprises an acrylate
content of from about 4% to about 40%, more preferably from about 5% to
about 35%, by weight, based on the weight of the E/AC/AA terpolymer, an
acrylic acid or methacrylic acid content of from about 1% to about 10%,
preferably 2% to 8%, by weight based on the weight of the E/AC/AA
terpolymer. The rest of the terpolymer is, of course, ethylene.
The E/AC/AA terpolymer may comprise a wide range of melt indexes (MI),
generally between about 0.1 to about 30, more preferably between about 1
to about 10, dg/min (ASTM D1238, Condition E).
Acrylates useful in the present invention are lower alkyl (meth) acrylate
esters. Lower alkyl as used in describing this invention means those alkyl
groups having from one to four carbon atoms. The preferred lower alkyl
acrylate is methyl acrylate.
The E/AC/AA terpolymer may be produced by any one of a number of well known
free radical initiated processes such as, for example, those described in
U.S. Pat. No. 3,350,372 which is incorporated by reference for all
purposes as if fully set forth. Generally ethylene, the (meth)acrylates
and the (meth)acrylic acids are metered into, for example, a high pressure
autoclave reactor along with any one of a number of well known free
radical polymerization initiators (catalysts) suitable for producing
ethylene and acrylic based polymers. Particularly preferred catalyst
include organic peroxides such as, for example, lauroyl peroxide, di-tert
butyl peroxide, tert butyl peroxide and various azo compounds. Typically,
the catalyst will be dissolved in a suitable organic liquid such as
benzene, mineral oil, or the like. Ordinarily the catalyst is used at a
level of between about 50 to about 20,000, more preferably between about
100 to about 250, ppm based on the weight of monomers.
The polyolefins, E/AC/AA terpolymer and/or blend may, if desired, include
one or more other well known additives such as, for example, antioxidants,
ultraviolet absorbers, antistatic agents, release agents, pigments,
colorants, or the like; however, this should not be considered a
limitation of the present invention.
The rubbers which can be compatibilized using these terpolymers, include,
but are not limited to, ethylene/ propylene rubber, neoprene, nitrile
rubber, ethylene/ propylene/diene terpolymers, SBR, butyl, halobutyl, poly
(isobutylene-co-4-Methylstyrene), poly(isobutylene-co-4-Bromomethyl
styrene), natural rubber and the like.
The term EPR or EPDM as used herein, unless otherwise indicated, includes
terpolymers, tetrapolymers, etc., preferably or ethylene, said C.sub.3
-C.sub.28 alpha-olefin and/or a non-conjugated diolefin or mixtures of
such diolefins which may also be used. The amount of the non-conjugated
diolefin will generally range from about 0.5 to 20 wt. percent, preferably
about 1 to about 7 wt. percent, based on the total amount of ethylene and
alpha-olefin present.
Representative examples of non-conjugated dienes that may be used as the
third monomer in the terpolymer include:
a. Straight chain acrylic dienes such as: 1,4-hexadiene; 1,5-heptadiene;
1,6-octadiene.
b. Branched chain acrylic dienes such as: 5-methyl-1,4-hexadiene;
3,7-dimethyl 1,6-octadiene; 3,7-dimethyl 1,7-octadiene; and the mixed
isomers of dihydro-myrcene and dihydro-cymene.
c. Single ring alicyclic dienes such as: 1,4-cyclo-hexadiene;
1,5-cyclooctadiene; 1,5-cyclododecadiene; 4-vinylcyclohexene; 1-allyl,
4-isopropylidene cyclo-hexane; 3-allyl-cyclopentene; 4-allyl cyclohexene
and 1-isopropenyl-4-(4-butenyl) cyclohexane.
d. Multi-single ring alicyclic dienes such as: 4,4'-dicyclo- pentenyl and
4,4'-dicyclohexenyl dienes.
e. Multi-ring alicyclic fused and bridged ring dienes such as:
tetrahydroindene; methyl tetrahydroindene; dicyclopentadiene; bicyclo
(2.2.1) hepta 2,5-diene; alkyl, alkenyl, alkylidene, cycloalkenyl and
cycloalkylidene norbornenes such as: ethyl norbornene; 5-methylene-6-
methyl-2-norbornene: 5-methylene-6, 6-dimethyl-2-norbornene:
5-propenyl-2-norbornene; 5-(3-cyclo-pentyl)-2-norbornene and
5-cyclohexylidene-2-norbornene; norbornadiene; etc.
The most preferred EPDM elastomer contains from about 60 to about 80% by
weight ethylene, from about 15 to about 35% by weight propylene and from
about 3 to about 7% by weight of non-conjugated diene. Synthesis of EPDM
is well known in the art. G. ver Strate, Encyclopedia of Polymer Science
and Engineering, vol. 6, 2nd Ed., 1986, p. 522-564.
The polychloroprene elastomer used as the major component in the elastomer
blend in one embodiment of the present invention is a commercially
available material, commonly referred to as CR or neoprene rubber. It is
available in a number of grades and molecular weights, all of which
elastomeric grades are suitable for use in the compositions of this
invention. The preferred grade is Neoprene GRT which is more resistant to
crystallization and is based on a copolymer of chloroprene and
2,3-dichloro-1,3-butadiene. Neoprene synthesis is also well known in the
art. C. A. Hargraves et al., Encyclopedia of Polymer Science and
Technology, vol. 3, p. 705-730.
The nitrile rubber used as the major component in the elastomer blend in
another embodiment of this invention is also a commercial material
available in a number of grades. Nitrile rubber is a random copolymer of a
major proportion of butadiene and a minor proportion of acrylonitrile and
is generally produced by free radical catalysis.
As indicated above, the polychloroprene or nitrile rubber preferably
constitutes the major component of the mixture of elastomers of the
present invention, but may be generally present in a range of from about
30 to 90% by weight based on total elastomer content.
It is also within the scope of the present invention to provide elastomer
compositions based on blends of the polychloroprene and nitrile rubber
components.
The vulcanizable composition of the present invention also includes a
conventional mixed vulcanizing system for EPR, polychloroprene and nitrile
rubber. Generally such vulcanizing systems include a metal oxide such as
zinc oxide, magnesium oxide and mixtures thereof, used either alone or
mixed with one or more organic accelerators or supplemental curing agents
such as an amine, a phenolic compound, a sulfonamide, thiazole, a thiuram
compound, thiourea or sulfur. Organic peroxides may also be used as curing
agents. The zinc or magnesium oxide is normally present at a level of from
about 1 to about 10 parts by weight per 100 parts by weight of elastomer
blend, and the sulfur and supplemental curing agents or curing
accelerators, where used, may be present at a level of from about 0.1 to
about 5 parts by weight per 100 parts by weight of elastomer blend.
The elastomer polymer composition may also contain other additives such as
lubricants, fillers, plasticizers, tackifiers, coloring agents, blowing
agents, and antioxidants.
Examples of fillers include inorganic fillers such as carbon black, silica,
calcium carbonate, talc and clay, and organic fillers such as high-styrene
resin, coumarone-indene resin, phenolic resins, lignin, modified melamine
resins and petroleum resins.
Examples of lubricants include petroleum-type lubricants such as oils,
paraffins, and liquid paraffins, coal tar-type lubricants such as coal tar
and coal tar pitch; fatty oil-type such as castor oil, linseed oil,
rapeseed oil and coconut oil; tall oil; waxes such as beeswax, carnauba
wax and lanolin; fatty acids and fatty acid salts such as licinoleic acid,
palmitic acid, barium stearate, calcium stearate and zinc laurate; and
synthetic polymeric substances such as petroleum resins.
Examples of plasticizers include hydrocarbon oils, e.g. paraffin, aromatic
and naphthenic oils, phthalic acid esters, adipic acid esters, sebacic
acid esters and phosphoric acid-type plasticizers.
Examples of tackifiers are petroleum resins, coumarone-indene resins,
terpene-phenol resins, and xylene/formaldehyde resins.
Examples of coloring agents are inorganic and organic pigments.
Examples of the blowing agents are sodium bicarbonate, ammonium carbonate,
N,N'-dinitrosopenta- methylenetetramine, azocarbonamide,
azobisisobutyronitrile, benzenesulfonyl hydrazide, toluenesulfonyl
hydrazide, calcium amide, p-toluenesulfonyl azide, salicyclic acid,
phthalic acid and urea.
The vulcanizable composition may be prepared and blended on any suitable
mixing device such as an internal mixer (Brabender Plasticorder), a
Banbury Mixer, a kneader or a similar mixing device.
The EP rubber or the EPDM is typically present at about 5 to 50 parts by
weight, more preferably 25 to 35 parts by weight, most preferably 30 parts
by weight. The terpolymer is typically present at 1 to 65 phr, more
preferably 5 to 20 phr, most preferably 10 phr. The CR or NBR is typically
present at 30 to 90 parts by weight, preferably 55 to 85 parts by weight,
more preferably 65 to 75 parts by weight, most preferably 70 parts by
weight. The carbon black may be present at from 3 to 50 parts per 100
parts rubber blend, preferably from about 20 to about 40 parts. Blending
temperatures and times may range from about 45.degree. to 180.degree. C.
and from about 4 to 10 minutes respectively. After forming a homogeneous
mixture of the elastomers and optional fillers, processing aids,
antioxidants and the like, the mixture is then vulcanized by the further
mixing-in of crosslinking agents and accelerators followed by heating the
resulting blend to a temperature of from about 100.degree. to 250.degree.
C., more preferably from about 125.degree. to 200.degree. C. for a period
of time ranging from about 1 to 60 minutes. Molded articles such as belts
and hoses are prepared by shaping the prevulcanized formulation using an
extruder or a mold, and subjecting the composition to temperatures and
curing times as set forth above.
The materials utilized in the examples are described below: (A) Neoprene
(CR) GRT is a polychloroprene made by DuPont. (B) Vistalon 7000 (abbr. V
7000) is a fast curing, high diene ethylene-propylene terpolymer (EPDM),
available from EXXON CHEMICAL COMPANY, with a Mooney viscosity
ML(1'4)@125.degree. C. of 60 and an ethylene content of 70 wt. %.
(C) Escor/ATX 350 an ethylene/methacrylate/acrylic acid terpolymer,
available from EXXON CHEMICAL COMPANY, comprising 24 wt. % methacrylate, 2
wt. % acrylic acid, 74 wt. % ethylene based upon the weight of the
copolymers.
(D) Escor/ATX 320 an ethylene/methacrylate/acrylic acid terpolymer,
available from EXXON CHEMICAL COMPANY, comprised of 18 wt. % methacrylate,
6 wt. % acrylic acid , 76 wt. % ethylene based upon the weight of the
copolymers.
(E) N650 and N762 are two well known, general purpose, moderately
reinforcing carbon blacks. They are standard as defined by ASTM D 1765-89
and are manufactured by a number of different companies including:
Continental Carbon, J. M. Huber, Phillips Chemical, Columbian Chemicals,
Cabot, and Ashland Chemical.
(F) Sundex 790 is a standard aromatic processing aid (oil) used for
compounding of a variety of rubbers: NR, SBR, CR, IIR, NBR, BR, EPM, EPDM.
Similar to the carbon blacks, it is manufactured by a number of companies:
Harwick, Matrochem, R. E. Carroll.
(G) Octamine is an antioxidant used primarily with CR, NBR, NR, and SBR. It
gives excellent protection against heat, oxygen, and flexing. Chemically,
it is a reaction product of diphenyl-amine and diisobutylene. It is
manufactured by Uniroyal Chemical.
(H) AgeRite HP-S is an antioxidant used in rubber compounding (similarly to
Octamine). It is a blend of dioctylated diphenylamines and
diphenyl-p-phenylene-diamine and is manufactured by R. T. Vanderbilt.
(I) Maglite D is a magnesium oxide, which is used as a curing agent in our
compound. It is manufactured by C. P. Hall and Merck Chemical.
(J) Paracil B is a nitrile rubber [poly(butadiene co-acrylonitrile)]
available from Uniroyal.
The foregoing more general discussion this invention will be further
exemplified by the following specific examples offered by way of
illustration and not limitation of the above-described invention.
The testing conditions and procedures used are set forth in Table A below.
TABLE A
______________________________________
Testing
Test Conditions Procedure
______________________________________
1. Mooney Viscosity
(1 + 8) @ 100.degree. C.
ASTM D 1646
(ML)
2. Mooney Scorch 132.degree. C.
ASTM D 1646
(MS)
3. Oscilating Disk
160.degree. C. +
ASTM D 2084-88
Rheometer (ODR)
3.degree. arc
No preheat
100 cycles/min
30 min rotor
4. Procedures for Pads Cured for
ASTM D 3182-89
mixing standard
20 min @ 160.degree. C.
compounds and
preparing standard
vulcanized sheets
5. Modulus, Tensile,
-- ASTM D 412
Elongation
6. Hardness (Durometer)
Shore A ASTM D 2240
7. Air Oven Age 140.degree. C. for 48
ASTM D 573
96 hr.
8. Static Ozone Bent Loop ASTM D 1149-86
Resistance 100 pphm ozone
37.8.degree. C.
9. Dynamic Ozone 100 pphm ozone
ASTM D 3395-86
Resistance 37.8.degree. C.
Method A
30 cycles/min
0-25% extension
10. Dynamic Crack 120.degree. C. flex
ASTM D 813-87
Growth angle
(De Mattia)* Room temp.
90.degree. C. flex
angle
100.degree. C.
11. Tel-Tak 24 oz., 60 sec,
Instruction
Room temp. Manual
Monsanto
Tel-Tak
Tester, July 1969
12. Melt Flow Rate (10 kg 230.degree. C.)
ASTM D 1238
13. Density ASTM D 792
______________________________________
*Specimens cured 25 min @ 160.degree. C.
EXAMPLES
Example 1
In an internal mixture (Banbury Intensive Mixer) were charged 100 part
polychloroprene (neoprene GRT) and all other ingredients listed in Table 1
(below) Example 1 except for the magnesium oxide and zinc oxide curing
agents. The temperature of the mixture was maintained at 100.degree.
C.-120.degree. C. and mixing was continued for a period of about 5
minutes. This intensive mixing included kneading, shearing, and cross-over
blending. The uniform admixture was then discharged from the Banbury and
placed on a two roll mill and milled at a temperature of 80.degree. to
90.degree. C. The zinc oxide/magnesium oxide curing agents were added to
the elastomeric mass and milling was continued for about 15 to 20 minutes.
The milled elastomer composition was then sheeted off the mill at a
thickness of about 0.1 inch, placed in a 6 inch by 6 inch by 0.075 inch
mold and cured at a temperature of about 160.degree. C. for a period of 20
minutes. The property evaluation of the molded samples were done using
standard test procedures shown in Table A.
Example 2
The process of Example 1 was repeated except that the elastomer composition
consisted of a mixture of 70 parts polychloroprene and 30 parts EPDM (V
7000). All other ingredients are as set forth in Table 1, Ex 2.
Example 3
The process of Example 1 was repeated except that the elastomer composition
consisted of a mixture of 70 parts polychloroprene, 30 parts EPDM and 10
parts Terpolymer ATX 350, the compatibilizer of this invention. Other
ingredients are set forth in Table 1, Ex 3.
As can be seen from the data included in Table 1, the beneficial effects of
compatibilization of CR/EPDM/Escor Acid Terpolymer ATX 350 (E-MA-AA),
70/30/10 alloys is evident in terms of significant improvements in heat
ageing (both tensile strength and elongation change), ozone resistance,
cut growth resistance and other physical properties. Addition of just EPDM
alone (i.e., Ex 2 in Table 1) decreased the tensile, elongation, and
abrasion resistance because of incompatibility of CR and EPDM. However,
adding small amounts (10 parts by weight) of the compatibilizer of this
invention, ATX 350, helped to bring these properties back up. In other
words, the CR/EPDM blend is "incompatible" and has poor physical
properties, while the CR/EPDM/E/AC/AA blend is a "compatible blend" and
has good physical properties.
The physical properties of the compatibilized blend (Ex. 3 in Table 1) are
generally superior both before and after exposure to heat, compared with
that of the non-compatibilized blend (Ex. 2 in Table 1). Addition of EPDM
to neoprene, in general, improved the ozone resistance. However, addition
of the compatibilizer of this invention, ATX 350, to CR/EPDM, 70/30 blend,
(Ex. 3 in Table 1) improved further the ozone resistance, specifically the
dynamic ozone resistance. In the cut growth resistance tests, the
compatibilized blend (Ex. 3 in Table 1) had vast improvement (lower the
numerical value, the better) compared with that of neoprene (Ex. 1 in
Table 1) and the binary blend (Ex. 2 in Table 1). This is a key property
for PTBs application.
TABLE I
__________________________________________________________________________
Formulations of Compounds:
Neoprene/EPR/
Neoprene Control
Neoprene/EPR
E/AC/AA
"CR" "A" "B"
Example 1
Example 2
Example 3
__________________________________________________________________________
Neoprene GRT 100 70 70
V7000 -- 30 30
ESCOR ATX 350
E/AC/AA Copolymer -- -- 10
VA-1801 -- -- --
N650 40 40 40
N762 30 30 30
Sundex 790 10 10 10
Stearic Acid 2 2 2
Octamine 2.5 -- --
Age Rite HP-S 0.5 -- --
Maglite D 4.0 4.0 4.0
Zinc Oxide 5.0 5.0 5.0
Mooney Viscosity (ML)
61 82 76
1 + 8 @ 100.degree. C.
Mooney Scorch (MS), 132.degree. C.
t.sub.3 (min) 7.8 8.3 5.5
t.sub.10 (min) 11.9 11.5 12.9
ODR, 160.degree. C. + 3.degree. arc
M.sub.L (lb(f)-inch)
10 17 16
M.sub.H (lb(f)-inch)
99 73 74
t.sub.s2 (min) 2.4 2.5 2.4
t.sub.c 90 (min) 17 16 12
Rate (slope) 19 12 11
Physical Properties
Cure 20 min @ 160.degree. C.
100% Modulus, MPa 7.5 6.9 8.2
200% Modulus, MPa 15.6 13.4 14.8
Tensile, MPa 19.0 15.4 16.5
Elongation, % 256 237 245
Hardness, Shore A 80 82 83
Air Oven Age, 48 hr A 140.degree. C.
Tensile, MPa 16.2 14.7 16.5
Elongation, % 115 149 172
Hardness, Shore A 88 88 87
Air Oven Age, 96 hr @ 140.degree. C.
Tensile, MPa 13.6 14.9 16.3
Elongation, % 49 95 109
Hardness, Shore A 90 90 90
Static Ozone Resistance
100 pphm O.sub.3, 37.8.degree. C., Bent Loop
Hours to 2x crack 8 >500 >500
Hours to visible crack
184 >500 >500
Dynamic Ozone Resistance
100 pphm O.sub.3, 37.8.degree. C.
0-25% Extension, 30 cycle/min
Hours to 2x crack 24 112 160
Hours to break 112 297 440
De Mattia Cut Growth
Average Crack Rate (inch/megacycles)
Room T, 120.degree. angle (0.50 in)
586 531 25
100.degree. C., 90.degree. angle (0.75 in)
938 891 15
Abrasion Resistance
92 81 92
Pico Index
__________________________________________________________________________
Nitrile Rubber (NBR)/EPDM/Escor Acid Blends
Nitrile rubber (NBR), Vistalon 7000 and Escor Acid ATX 320 were compounded
using a small scale (45 cc) Brabender mixer. The blend compositions are
listed in Table 3 below. Blend samples were examined in the optical
microscope as thin section (100-200 nm) using phase contrast. The NBR
phase appeared dark grey and the V 7000 or Escor Acid Terpolymer phase
appeared white. The Photomicrographs showed Escor Acid ATX 320 seems to
have better interaction with NBR which resulted in better dispersion of
the terpolymer in NBR matrix. This is also evident in the phase morphology
of NBR/V 7000/Escor Acid Terpolymer ATX 320, 70/20/10 blend which had
better dispersion (i.e. more surface area) of the V 7000 phase in NBR
matrix.
TABLE 3
______________________________________
NBR/V 7000/ESCOR ACID TERPOLYMERS BLENDS
Blend Components
Blends # (Paracril B) V 7000 ATX 320
______________________________________
1 70 30 --
2 70 30 5
3 70 20 10
4 70 -- 30
______________________________________
Neoprene/EPDM/Escor Acid/Carbon Black Blends
Neoprene, Vistalon 7000, and ATX 350 were compounded in a ratio with
7/30/10 with carbon black (Ex 3 in Table 1). Transmission electron
microscopic (TEM) technique was further utilized to characterize carbon
black dispersion in these blends. Since large differences in unsaturation
exist between neoprene and EPDM, we used osmium tetroxide staining in our
TEM studies. This staining technique rendered the higher unsaturation
neoprene polymer, more opaque to provide contrast for TEM analysis.
Analysis of TEM data indicated the following:
Carbon black localized selectively in neoprene phase in the control blend
of 70/30 neoprene/EPDM--CR GRT/ V 7000 (Ex 2 in Table 1). A phase boundary
existed between neoprene phase (which is "opaque") and EPDM phase (which
is "light"). Since the carbon black aggregates localized in neoprene
phase, the neoprene phase size increased and the "opaque/light" area ratio
appears bigger than the corresponding blend of 70/30 neoprene/EPDM.
When the acid terpolymer was blended in to achieve at 70/30/10,
neoprene/EPDM/ATX 350 ratio, carbon black dispersion was noted in both the
neoprene (opaque) and EPDM (light) phases. A completely different
morphology was noted, in particular, the neoprene phase size was not as
big as in the control. Good phase boundary existed between the phases,
however.
The composition of the two blends are listed in Table 1.
As is apparent from the foregoing description, the materials prepared and
the procedures followed relate to specific embodiments of the broad
invention. It is apparent from the foregoing general description and the
specific embodiments that, while forms of the invention have been
illustrated and described, various modifications can be made without
departing from the spirit and scope of this invention. Accordingly, it is
not intended that the invention be limited thereby.
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